The objective of this research is to test the idea that cellular senescence results from a loss in temporal organization of biosynthetic and degradative processes with the consequent arrest and differentiation of cells in inappropriate portions of the cell cycle. In pursuing this problem it became apparent that it would be necessary to synchronize WI- 38 cells in order to resolve the questions asked. An automated- synchrony apparatus has been constructed which synchronizes by mitotic selection. Since the cells are grown in roller bottles and since the selection conditions (speed of revolution) can be optimized, reasonable numbers of mitotic cells can be selected. Our work will attempt to establish that enzyme oscillations are a characteristic of normal diploid fibroblasts and in fact are more pronounced in such cells than in established and neoplastic cells. One testable consequence of the loss of temporal order may be the arrest of WI-38 cells in portions of the cell-cycle which are refractory to rescue by the usual procedures of subculturing, serum and serum-factor stimulation.